The present invention relates to a device for multiplexing or demultiplexing several light signals in integrated optics. It is more particularly used in the fields of processing radar signals in real time, optical telecommunications, optical fiber sensors, etc.
The multiplexing of light signals of different wavelengths in integrated optics is very important in optical telecommunications, because it makes it possible to carry within the same optical fibre a large information quantity with constant pass bands.
A demultiplexing device or demultiplexer in integrated optics makes it possible to separate n light signals of different wavelengths carried by the same first optical fiber and respectively inject said n light signals into n second optical fibers. Conversely, a multiplexing device or multiplexer makes it possible to regroup into a single beam, n light signals of different wavelengths respectively from n optical fibers.
In such devices, two major problems occur. The first problem is to ensure the multiplexing function, i.e. at the output of the device the ith second optical fiber, i being an integer between 1 and n, may only carry the wavelength .lambda..sub.1, to within .DELTA..lambda./2. Thus, the ideal multiplexing element is a square wave pulse filter of width .+-..DELTA..lambda./2 and of transmission 1 if .lambda..sub.i -.DELTA..lambda./2&lt;.lambda.&lt;.lambda..sub.i +.DELTA..lambda./2, which would reflect or conversely transmit in a perfect manner the light signals whose wavelengths are not in said range and conversely would transmit or reflect those whose wavelengths are within said range. A succession of such filters would form the ideal multiplexer.
The second major problem is the coupling of the multiplexer with generally monomode optical fibers carrying light informations. Thus, the light losses at the input and output of the multiplexer must be as small as possible.
In the presently known multiplexers in integrated optics, the multiplexer function, i.e. the chromatic dispersion of the different light signals is ensured by a grating, as in conventional optics. Such a multiplexer is more particularly described in an article in Applied Optics, vol. 21, no. 12,of June 15, 1982, pp. 2195 to 2198 by T. SUHARA et al entitled "Integrated-Optic Wavelength Multi- and Demultiplexers Using a Chirped Grating and an Ion-Exchanged Waveguide".
Unfortunately, these multiplexers do not solve the most important problem regarding the coupling of the multiplexer and monomode optical fibers used for carrying light information, as well as that of the collimation of the light beam, which acts on the dispersive element or grating of the multiplexer.